Download the codec. Though there are several sites that provide opensource codecs for free, there are few that provide closed source too. I have found Final build site to be quite good and provides almost all codecs. If you dont have any codecs at all I do suggest you to install Klite codec Pack and have some basic codecs to start with.

Step 3:

If you have started using Media Player classic without any change then you are most probably using FFmpeg codecs. These are very good codecs and use libavcodec for most of the decoding. It decodes most formats however not all of them perfectly. Now that you have your new filter installed.

Open the options window in media player classic(by pressing ‘o’ or through right click menu )

Go to External filters option. Now in the right side of the window select Add Filter

You will get an elaborate window with a plethora of options. Select your codec

If your codec is not available there you will have to put a little more stress. Open the folder that your codec installed in.

find a file with .ax extension in that folder and put it in filters folder inside Klite Codec Pack folder

Now you should click browse in the bottom left of codec window and select the filter inside filters folder. You can browse to select ax file from the folder it was installed but needlessly adds a dependency.

After selecting that filter go the right of the window and click Prefer among the 3 options(prefer, block and merit)